Thermal chamber for a developability regulating apparatus

ABSTRACT

An apparatus in which the developability of an electrophotographic printing machine is regulated. Errors induced by temperature fluctuations are minimized by controlling the thermal environment.

United States Patent 11 1 Whited 1 July 1, 1975 THERMAL CHAMBER FOR ADEVELOPABILITY REGULATING APPARATUS [75] Inventor: Charles A. Whited,Rochester, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Jan. 30, 1974 [21] App]. No.1 438,126

Related US. Application Data [62] Division of Ser. No. 295,775, Oct. 6,1972, Pat. No,

[52] US. Cl. 250/227; 250/238; 250/239 [51] Int. Cl. G02b 5/14 [58]Field of Search 250/227, 238, 239; 355/10, 355/3 DD; 356/201, 202, 203

[56] References Cited UNITED STATES PATENTS 3,327,126 Shannon 250/2383,558,895 1/1971 Harlmann 250/227 3,737,629 6/1973 See 250/227 3,790,7912/1974 Anderson 250/238 3,792,284 211974 Kaelin 250/227 3,800,147 3/1974Shea 260/238 Primary Examinerlames W. Lawrence Assistant ExaminerD. C.Nelms Attorney, Agent, or FirmH. Fleischer; .1. .1. Ralabate; C. A.Green [57] ABSTRACT An apparatus in which the developability of anelectrophotographic printing machine is regulated. Errors induced bytemperature fluctuations are minimized by c0ntr01ling the thermalenvironment.

4 Claims, 5 Drawing Figures ISTS W JUL 1 SHEET THERMAL CHAMBER FOR ADEVELOPABILITY REGULATING APPARATUS This is a division. of applicationSer. No. 295,775, filed Oct. 6, I972. now U.S. Pat. No. 3.817.6l6 issuedto Whited in I974v BACKGROUND OF THE INVENTION This invention relatesgenerally to an clectrophotographic printing machine, and moreparticularly concerns means for maintaining the thermal environment of aphotosensor utilized in a developability regulating apparatussubstantially at a predetermined temperature in order to minimize systemerrors.

In the process of electrophotographic printing a developer mix ofcarrier granules and toner particles is used to form a toner powderimage of an original document on sheet material. The developabilityregulating apparatus adjusts the characteristics of the developer mix toproduce toner powder images having suitable density and color balance,i.e. developability. Developability is related to the concentration oftoner particles in the developer mix, i.ev the ratio of toner particlesto carrier granules. Environmental conditions such as temperature andhumidity conditions effect developability. The physical parameters ofthe development system also effect developablitlty, e.g. spacing.electrical bias, mass flow rate and the magnetic field, amongst others.Furthermore, the electrical attraction between the toner particles andcarrier granules influences developability. Toner particle concentrationwithin the developer mix is controlled to maintain image density andcolor balance at an appropriate levelv A system utilizing thedevelopability apparatus of the present invention is described, indetail, in U.S. Pat. No. 3,754,821 issued to Whited in I973 and assignedto the assignee of the present invention.

The thermal environment surrounding the photosensor is subject totemperature transients. This is due, in part. to localized heating bysuch sub-components as the fuser which is incorporated in the printingmachine to permanently fix the powder image to the support material.Moreover. heat from scan lamps and electrical power supplies, as well asthe air flow generated by the blowers produce thermal transients whichmay rapidly change the temperature in the region surrounding thephotosensor. Photosensors utilized in developability regulatingapparatus are frequently sensitive to temperature variations. Forexample, at 4C change in the photosensor temperature causes thedevelopability regulating mechanism to indicate that there is anincorrect concentration of toner particles in the developer mix.

It is, therefore, a primary object of the present invention to improvethe thermal environment of the photosensor incorporated in thedevelopability regulating apparatus of electrophotographic printingmachine.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with thepresent invention, there is provided an apparatus for maintaining thethermal environment of a photosensor substantially at a predeterminedtemperature.

This is accomplished in the present instance by an open ended containerdefining an internal chamber for housing the photosensor therein. One ofthe features of the present invention is to transmit light rays to thephotosensor by means of a fiber optic light pipe. Hence, in thepreferred ebodiment, provision is made in an end cap of the container toaccommodate the light pipe. The end cap forms, in conjunction with thelight pipe, a substantially heat-tight joint. Means are provided forheating the container to a predetermined temperature, and forcontrolling the heating means such that the container remainssubstantially at the predetermined temperature.

The present invention is also concerned with minimizing errors due tothermal variations in the photosen sor used in the developabilityregulating apparatus of an electrophotographic printing machine. Inperforming this function, the photosensor detects modulated light raysto indicate the density of toner particles electrostatically adhering totransparent electrode means. This corresponds to the density of tonerparticles being deposited on an electrostatic latent image recorded on aphotoconductive member. In order to minimize errors in the regulatingapparatus, the photosensor is disposed in a thermally controlledenvironment. Hence, the photosensor is housed in the previouslydiscussed container and is maintained substantially at a predeterminedtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will become apparent upon reading the followingdetailed description and upon reference to the drawings in which:

FIG. 1 is a schematic perspective view of an electrophotographicprinting machine embodying the features of the present inventiontherein;

FIG. 2 is a sectional elevational view of a photoconductive drum used inthe FIG. 1 printing machine, and showing, in detail, the apparatus ofthe present invention;

FIG. 3 is a sectional elevational view of the apparatus of the presentinvention;

FIG. 4 is an enlarged, exploded perspective view of the photosensormounting arrangement incorporated in the FIG. 3 apparatus; and

FIG. 5 is an enlarged, perspective view of the FIG. 4 mountingarrangement.

While the present invention will be described in con nection with apreferred embodiment, it will be understood that it is not intended tolimit the invention to that ebodiment. On the contrary, it is intendedto cover all alternatives, modifications and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawingswherein like reference numerals have been used throughout to designatelike elements, FIG. I schematically illustrates an electrophotographicprinting machine adapted to reproduce muIti-color copies from a coloredoriginal document. The printing machine depicted in FIG. 1 utilizes aphotoconductive member having a rotatably mounted drum 10 with aphotoconductive surface 12. Drum I0 is arranged to rotate in thedirection of arrow 14 and moves photoconductive surface 12 sequentiallythrough processing stations A through E, inclusive.

Drum I0 initially rotates photoconductive surface I2 through chargingstation A. A corona generating device. depicted generally at I6, extendstranvfersely across photoconductive surface 12. By being positioned inthis orientation, corona generating device 16 is capable of chargingphotoconductive surface 12 to a relatively high uniform potential. Asuitable corona generating device 16 is described in U.S. Pat. No.1778,9 46 issued to Mayo in l957.

Thereafter, charged photoconductive surface 12 rotates to exposurestation B which includes thereat a moving lens system, designatedgenerally by the reference numeral 18, and a color filter mechanism,indicated generally at 20. Original document 22 is stationarilysupported face down upon transparent platen 24. Lamp assembly 26 andlens system 18 are moved in timed relation with photoconductive surface12 to produce a flowing light image of the original document onphotoconductive surface 12. During exposure. filter mechanism interposesselective color filters into the optical light path of lens 18. Thecolor filter operates on the light passing therethrough to record anelectrostatic latent image on photoconductive surface 12 correspondingto a spectral region of the electromagnetic wave spectrum i.e. a colorseparated latent image.

After the electrostatic latent image has been recorded onphotoconductive l2. drum 10 rotates to development station C.Development station C includes three individual developer unitsgenerally indicated by the reference numeral 28, 30 and 32,respectively. Each developer unit contains toner particles of aspecified color. The developer unit having toner particles appropriatefor the filter utilized develops the clectrostatic latent image recordedon photoconductive sur' face 12. Preferably. developer units 28, 30 and32 are all of a type generally referred to in the art as magnetic brushdevelopment units." In a typical magnetic brush development system, amagnetizable developer mix having carrier granules and toner particlesis con tinually brought through a directional flux field forming a brushof developer mix. Development is achieved by bringing the brush ofdeveloper mix into contact with photoconductive surface l2. Each of therespective developer units 28. 30 and 32 apply toner particlescorresponding to the complement of the color separated electrostaticlatent image recorded on photoconductive surface 12.

Having been developed, the powder image electroitatically adhering tophotoconductive surface 12 is advanced to transfer station D. Attransfer station D. the aowder image is transferred to a sheet of finalsupport naterial 34, e.g. plain paper or a thermoplastic trans- )arencyamongst others, by means of a biased transfer 'oll, shown generally at36. Transfer roll 36 is biased electrically to a potential of sufficientmagnitude and aolarity to electrostatically attract toner particles fromahotoconductive surface 12 to support sheet 34. A single sheet of finalsupport material 34 is supported on .ransfer roll 36. Roll 36 isarranged to move in synchroiism with photoconductive surface 12 and isadapted o recirculate support material 34 for a plurality of cyrles.i.e. 3 cycles. In this manner successive toner powier images, eachcorresponding to a specific color in he electromagnetic wave spectrum.are placed in su )erimposed registration upon support material 34.-lence. it is apparent, that in this way a multi-color :opy isreproduced from the colored original.

Support material 34 is stripped from roll 36 and Jassed to a fusingstation (not shown) where the pow ler image is coalesced thereto.

The final processing station in the direction of rotation of drum It),as indicated by arrow 14, is cleaning station E. A rotatably mountedfibrous brush 38 is positioned at cleaning station E, and is maintainedin engagement with photoconductive surface 12 of rotating drum 10. Inthis way, residual toner particles remaining on photoconductive surface12 are removed therefrom.

Additional toner particles are added to the respective developer unitwhen developability, as hereinbefore described. is no longersatisfactory. The developability regulating apparatus, indicatedgenerally at 40, includes transparent electrode means 42, illuminatingmeans or light source 44, and sensing means or photosensor 46. Duringdevelopment, toner particles are deposited on electrode 42 and theintensity of the light rays transmitted therethrough is indicative ofthe density thereof. Fiber optic light pipe 48 directs the modulatedlight rays to photosensor 46. Photosensor 46 is mounted within heatingapparatus 50 to minimize ther mal fluctuations due to temperaturevariations. Suitable logic circuitry compares the electrical outputsignal from photosensor 46 with a reference to determine whether or nottoner particles should be dispensed to the appropriate developer unit,i.e. yellow toner parti cles to developer unit 28, magenta tonerparticles to developer unit 30, cyan toner particles to developer unit32.

Turning now to FIG. 2, there is shown the detailed construction ofregulating apparatus 40. Transparent electrode 42 is mounted onphotoconductive surface 12 in the non-image portion thereof. Electrode42 in cludes a glass window 52 having a transparent tin oxide coatingthereon. Electrically conductive glass of this nature is made byPittsburgh Plate Glass under the trademark NESA or by Corning GlassCompany under the trademark Electro-Conductive. A generally tubularmember threadedly engages an aperture in the circumferential surface ofdrum l0 and is arranged to align light source 44 mounted therein withglass 52. As shown in FIG. 2, light source 44 is mounted on plate 56which, in turn. is mounted slidingly in tubular member 54. Plate 56engages undercut 58 in tubular member 54 and is positioned thereby, Lockscrew 60 secures plate 56 in the aforementioned position. Suitable leadwires 62 extend from light source 44 and are interconnected with leadwires 64 which pass through the hollow core of shaft member 66. Shaftmember 66 is adapted to support drum l0 rotatably. Lead wires 66 areinterconnected to slip ring assembly 68 which transmits a regulatedcurrent from voltage regulator 70. Voltage regulator 70 receives anunregulated input of between 8 and [0 volts and adjusts theaforementioned input to a regulated output preferably. of about 5 voltsfor exciting lamp 44.

Referring once again to FIG. 2, an electrical biasing voltage is appliedto transparent electrode 42 through slip ring 68. Preferably. thisvoltage simulates the electrostatic latent image recorded onphotoconductive surface [2. The voltage is automatically applied totransparent electrode 42 via the position of drum 10 with respect toslip ring assembly 68. Hence, prior to entering the development zone avoltage of about 200 volts above developer bias, which is preferablyabout 500 volts. is applied to transparent electrode 42. As drum 10rotates into the development zone. the magnetic brush assembly of therespective developer unit applies toner particles to transparentelectrode 42.

Toner particles are attracted to transparent electrode 42 by the voltagedifferential of approximately 200 volts between electrode 42 and thecorresponding developer unit. The biasing voltage is removed fromelectrode 42 as it reaches cleaning station E permitting brush 38 toremove the remaining toner particles therefrom. The light raystransmitted through electrode 42 are guided by fiber optic light pipe 48to photosensor, or photocell 46, disposed within heating apparatus 50.Preferably, glass fiber optics are used to obtain good transmittance inthe near infrared region. Glass fiber optics do not attenuate radiantenergy in the most sensitive region of the silicon phototransistor.which is the preferred photocell.

Fiber optic light pipe 48 is mounted in plenum chamber 72 by suitablemounting means, e.g. a clamp. Positive lamina flow is directed into thechamber to purge the system and reduce particle contamination therein.As shown in FIG. 2, fiber optic light pipe 48 extends into heatingapparatus 50 through a heat-tight aperture therein to conduct modulatedlight rays transmitted through electrode 42 to photosensor 46 mountedtherein. Photosensor 46 and the associate circuit elements are allmounted within heating apparatus 50. In this manner, both photosensor 46and the associate circuit elements are maintained at a temperatureranging from about 50C to about 60C, the temperature preferably beingabout 55C. This arrangement minimizes thermal fluctuations in thesurrounding environment and substantially reduces the system errors dueto the temperature sensitivity of photocell 46.

Preferably, photocell 46 is a suitable silicon phototransistor such asthat produced by the General Electric Co. Model No. LI4B. It should benoted that this type of photocell requires a controlled thermalenvironment to minimize errors. For example, a 4C change in temperaturein the surrounding environment of photocell 46 will produce an errorsignal indicating an incorrect concentration of toner particles withinthe developer mix. Thus, it is highly desirable to maintain the thermalenvironment of photocell 46 substantially constant. This isaccomplished. in the present instance by heating apparatus 50 of thepresent invention. The foregoing heating apparatus 50 will be describedin greater detail with reference to FIGS. 3 through 5, inclusive.

Turning now to FIG. 3, there is shown, in detail heating apparatus 50.Temperature maintaining means or heating apparatus 50 includes an openended container 74. Container 74 defines an internal chamber 80 forhousing photosensor 46 therein. Container 74 is insulated and includessuitable circuitry and heating elements for maintaining interior chamber80 at a suitable temperature. Control circuitry and heating elements 76are disposed within container 74. By way of example, a thermistorfunctioning as one leg of a Wheatstone bridge may be used to detecttemperature variations. This type of Wheatstone bridge arrangement maycontrol wire wound resistance heating elements. Wall 78, interposedbetween the control circuitry and heating elements disposed in internalchamber 80, has a slot 82 therein for receiving a generally planarsupport member or printed circuit board 84. Disc member 86 isintermeshed with printed circuit board 84 to align lens 88 therein withphotosensor 46 mounted on printed circuit board 84. The detailedassembly of disc member 86 with printed circuit board 84 will bedescribed hereinafter with reference to FIGS. 4 and 5.

Referring once again to FIG. 3, end cap 90 is secured to container 74 onthe open end thereof. End cap 90 is permanently affixed by suitablemeans, eg cement, to the open end of container 74 to form a heat'tightjoint therebetween. A plurality of substantially equally spacedprotuberances 92 (in this case 8 pins) extend from end cap 90 in adirection substantially parallel to the longitudinal axis thereof. Inaddition, thereto, end cap 90 includes aperture 94 which issubstantially circular to receive end portion 96 of fiber optic lightpipe 48. Flanged member 98 includes an aperture 100 therein permittingthe fiber optic light pipe 48 to pass therethrough such that end portion96 extends therebe' yond. Moreover, flanged member 98 includes aplurality of equally spaced apertures (in this case 8 holes extendingpartially therethrough substantially parallel to the longitudinal axisthereof) for receiving pins 92 of end cap 90. Thus, in operation fiberoptic light pipe 48 is secured in a heat-tight fashion to flanged member98 by passing through aperture I00 therein. Fiber optic light pipe 48is, thereafter, assembled to container 74 by passing end portion 96slidingly into aperture 94 of end cap 90. Pins 92 mate with holes 94 toform a substantially heat-tight joint therebetween, Hence, in thisfashion modulated light rays are guided from transparent electrode 42 tolens 88 which focuses the aforementioned modulated light rays ontophotocell 46 for measuring the intensity thereof.

Turning now to FIG. 4, there is shown an exploded perspective view ofdisc member 86 being assembled to circuit board 84. As depicted therein,disc member 86 includes substantially circular opening 104 for securingthereto lens 88. Furthermore, disc member 86 includes a slot 106extending from the circumferential surface thereof partiallytherethrough being positioned transversely a radius chord thereof. Discmember 86 is adapted to intermesh with printed circuit board 84. Inorder to accomplish this, printed circuit board 84 also includes a slot108 extending from one surface thereof partially therethrough.

Disc member 86 is assembled to board 84, as shown in FIG. 5, byintermeshing slot 106 therein with slot 108 in printed circuit board 84.In this manner, the composite assembly of disc member 86 and board 84forms an integral support with aperture 104 properly aligned such thatwhen lens 88 is disposed therein light rays passing therethrough arefocused on photocell 46.

By way of example, the aforementioned heating apparatus 50 is arrangedto raise the temperature of the internal chamber thereof, whereinphotosensor 46 is positioned, from about 60F to about 55C within aboutthree minutes. Heating apparatus 50 is excited by a suitable 24 volt DCinput. The aforementioned control apparatus, hereinbefore described asbeing proportional, may also be of a suitable on-off type.

Thus, in recapitulation, heating apparatus 50 of the present inventionmaintains photosensor 46 in a substantially constant thermal environmentto substantially minimize temperature fluctuations thereof. In this way,thermal errors induced in the development regulating apparatus aresubstantially reduced. Moreover. heating apparatus 50 is adapted topermit fiber optic light pipe 48 to pass therethrough and guide themodulated light rays from transparent electrode 42 to photosensor 46.The aforementioned fiber optic light pipe 48 7 is automatically alignedin heating apparatus 50 with lens 88 to focus the light rays passingthercthrough onto photosensor 46.

it is. therefore, apparent that there has been provided in accordancewith this invention, an apparatus for minimizing thermally inducederrors in a developability regulating apparatus that fully satisfies theobjects. aims and advantages set forth above. While this invention hasbeen described in conjunction with specific embodiments thereof. it isevident that many alernatives. modifications and variations will beapparent to those skilled in the art. Accordingly, it is intended toembrace all alternatives. modifications and variations that fall withinthe spirit and broad scope of the appended claims.

What is claimed is:

I. An apparatus for controlling the thermal environment of a photosensoradapted to detect light rays emitted from a light source, including:

a fiber optic light pipe for transmitting light rays to the photosensor;

an open ended container defining an internal chamber for housing thephotosensor;

an end cap having an aperture therein adapted to receive one end portionof said fiber optic light pipe to form therewith a substantiallylight-tight joint, said end cap being mounted on the open end of saidcontainer to form therewith a substantially heat-tight joint;

means for heating said container to a predetermined temperature; and

means for controlling said heating means such that said containerremains substantially at the predetermined temperature.

2. An apparatus as recited in claim I, wherein:

said end cap includes a plurality of substantially equally spacedprotuberances extending therefrom in a direction substantially parallelto the longitudinal axis thereof; and

said fiber optic light pipe includes a flanged member having an aperturetherein permitting the other end portion of said fiber optic light pipeto pass therethrough and extend therefrom forming a substan tiallyheat-tight joint therewith, said flanged memher having a plurality ofsubstantially equally spaced openings therein arranged to receive saidprotuberances extending from said end cap.

3. An apparatus as recited in claim 1 further including:

a disc member having an aperture therein and an open ended slotextending over a portion of said disc member substantially transverse toa radius thereof spaced from the aperture therein;

a generally planar support member having mounted thereon saidphotosensor said support member having an open ended slot thereinadapted to intermesh with the corresponding slot in said assembly.member to form a unitary assembly said disc member being positionedsubstantially normal to said support member; and

a lens member mounted in the aperture of said disc member and arrangedto focus the light rays transmitted through said fiber optic light pipeonto said photosensor for measuring the intensity thereof.

4. An apparatus as recited in claim 3, wherein the predeterminedtemperature ranges from about 50C to about 60C preferably being about55C.

1. An apparatus for controlling the thermal environment of a photosensoradapted to detect light rays emitted from a light source, including: afiber optic light pipe for transmitting light rays to the photosensor;an open ended container defining an internal chamber for housing thephotosensor; an end cap having an aperture therein adapted to receiveone end portion of said fiber optic light pipe to form therewith asubstantially light-tight joint, said end cap being mounted on the openend of said container to form therewith a substantially heat-tightjoint; means for heating said container to a predetermined temperature;and means for controlling said heating means such that said containerremains substantially at the predetermined temperature.
 2. An apparatusas recited in claim 1, wherein: said end cap includes a plurality ofsubstantially equally spaced protuberances extending therefrom in adirection substantially parallel to the longitudinal axis thereof; andsaid fiber optic light pipe includes a flanged member having an aperturetherein permitting the other end portion of said fiber optic light pipeto pass therethrough and extend therefrom forming a substantiallyheat-tight joint therewith, said flanged member having a plurality ofsubstantially equally spaced openings therein arranged to receive saidprotuberances extending from said end cap.
 3. An apparatus as recited inclaim 1 further including: a disc member having an aperture therein andan open ended slot extending over a portion of said disc membersubstantially transverse to a radius thereof spaced from the aperturethErein; a generally planar support member having mounted thereon saidphotosensor, said support member having an open ended slot thereinadapted to intermesh with the corresponding slot in said assembly,member to form a unitary assembly said disc member being positionedsubstantially normal to said support member; and a lens member mountedin the aperture of said disc member and arranged to focus the light raystransmitted through said fiber optic light pipe onto said photosensorfor measuring the intensity thereof.
 4. An apparatus as recited in claim3, wherein the predetermined temperature ranges from about 50*C to about60*C, preferably being about 55*C.